Patent GB-1447587-A (GB)
Title: Film projector
IPC: G03B35/24
Filed: 1974-04-11
Abstract: 1447587 Film projectors VANGUARD INSTRUMENT CORP 11 April 1974 [11 July 1973] 16270/74 Heading G2E A projector is constructed so that it produces a projected image of substantially the same intensity, and free of flicker, for different modes of operation. The four modes of projection envisaged are (a) still frame, (b) single frame advance, (c) low speed projection, and (d) normal or high speed projection. As shown, the film drive derives from a motor 39 which drives two output shafts 37 and 42. Shaft 37 rotates at a constant relatively high speed, and shaft 42 can be controlled by clutches not shown, to rotate at high speed, low speed, or to remain unclutched. Shaft 37 is connected by a slip clutch 41 to the two-bladed shutter 33. Shaft 42 drives, via a chain 44, the main shaft 45. This drives, via a worm 47 and gear 48, film sprockets 21, 22 so that loops 31, 32 are maintained in the film. Shaft 45 also drives, via gears 51, 52, a mechanism 55 operating the cam arrangement 56, 57 which actuates the pawl 36 engaging the film for intermittent transport past the projection aperture 27 Mechanism 55 includes an arm 74 which can be shifted about a pivot 75 by means of a solenoidoperated linkage 77, 78 from position B, in which shafts 73 and 53 are in alignment, to position D, in which they are out of alignment. The two shafts are carried by respective members 69, 72, connected by a slide block 71. In position B, members 69 and 72 rotate in unison throughout. In position D there is a portion of each revolution during which member 72 has a higher angular speed than member 69, and during this period of acceleration pawl 36 advances the film. In mode (a) shaft 37 rotates shutter 33 at high speed (1460 rpm) through clutch 41. Shaft 42 is unclutched, so that the film advance mechanism is not operated. In mode (b), shaft 42 is actuated at low speed (240 rpm), and shift arm 74 is offset to position D, so that the single frame advance is very rapid and not detected by the observer. Shutter 33 continues to rotate so that illumination remains constant. After a single revolution, shaft 42 is declutched. In mode (c) shift arm 74 is again offset to position D. Shaft 42 again rotates at low speed (240 rpm), and its motion is transmitted via belt 44 to shaft 45. A sprocket 65 which can be clutched to shaft 45 is driven at a 1:6 ratio by a sprocket 67 which is keyed to the shutter shaft. Thus the two parts of clutch 50 are at relatively similar speeds, and so readily clutch togather. When this occurs, slip clutch 41 is over-ridden and accommodates the slight difference between shutter 33 and shaft 37. Since shift arm 74 is offset, each actual film frame advance is very rapid, so that no flicker is observed. In mode (d) shift arm 74 is in position B, so that no acceleration of film advance is provided. Shaft 42 rotates at the high speed (1440 rpm). Clutch 50 is disengaged, but a clutch 64 on an auxiliary shaft 63, driven at the same speed as shaft 45, is engaged, which drives a sprocket 66 chain-connected to sprocket 67 on the shutter shaft. The shutter is thus synchronized with the film advance mechanism.